JS array (summary)

Like what to introduce Algorithm 、 What is the data structure , I'll stop talking , Go straight to the point

js Array is used in , Namely Call directly API, You don't have to package it yourself

The reason why encapsulation is not needed

1. Almost all programming languages Natively supports array types , Because arrays are the simplest memory data structures
2. js The array of is not like c Language is the same as the underlying code , Only data types other than those defined can be stored , It won't define how long it is and can't increase by itself

The disadvantages of arrays

1. Insert... In the middle position 、 The efficiency of deleting elements is relatively low , Because Move elements
2. Array expansion , Some languages need Reapply for more storage space , After assigning all the original values , Remove the original array

Create array

Array methods – Return value

js The array of provides many methods ：

Of course, there is something missing ：

pop（ Delete the last element ）-- Return removed items

push（ Add element at the end ）-- Returns the length of the modified array

shift（ Delete first element ）– Return removed items , If the array is empty, it returns underfined

unshift（ Add an element before the first element ）– Returns the length of the array

splice（ The most powerful method ）– The operation passes different parameters and returns different , It's hard to describe

And some missing higher-order functions , for example ：

reduce（ Ergodic summation ）– Returns the result of the sum

filter（ Traversal array , Filter the qualified array elements ）– Return the qualified New array

sort（ Array From small to large / From big to small array , Letters can also ）– Return to the changed Original array

find（ Find the first qualified member ）– Return array members

fundIndex（ Find the first index that matches the member ）– Return index value

I won't say more here , You can see it directly ：
data structure ( Two ) Array structure of
Higher order function - - Liao Xuefeng
05 vue Which array operations of are responsive
js Array method and its return value ( It is easy to use )

Array method note

One 、toString and valueOf The difference between

toString() and valueOf() All are Object method .toString() Method returns the string that reflects the object .valueOf() Method if any original value exists , It converts the object to its original value by default ; Object is a compound value , Most objects cannot really be represented as an original value , So by default valueOf() Method simply returns the object itself , Instead of returning a raw value .

See my blog here ：2021 Yahong interview question 2

1. toString() and valueOf() The main difference is ,toString() The returned string is , and valueOf() The return is The original object

2. because undefined and null Not object , So they toString() and valueOf() There are no two methods

3. The number Number Type of toString() The method can connect Receive conversion base , Returns a numeric value in the form of a string with different base numbers ; and valueOf() Method cannot accept conversion cardinality

4. Time Date Type of toString() Method String representing time Express ; and valueOf() Method returns from now to 1970 year 1 month 1 Japan 00:00:00 Of the numeric type Number of milliseconds

5. The object of the package valueOf() Method returns the original value of the wrapper object

6. Use toString() Method to distinguish between built-in functions and custom functions

Thanks to the author ： Rice next door , The article links ：https://www.jianshu.com/p/24547d4e565f

Two 、pop|push|shift|unshift

These methods can accept multiple parameters , Add or remove multiple elements at once ！